[Feature Request] Add document layout analysis confidence scores

## Feature Description Include confidence scores for each extracted element to help downstream processing decide which elements to trust. ## Use Case In our enterprise RAG pipeline, we process thousands of PDFs daily. Some elements are extracted with low confidence (rotated tables, scanned handwritten notes). Having confidence scores would let us: 1. Filter out low-confidence extractions 2. Route uncertain elements to manual review 3. Weight chunk importance in retrieval ## Current Behavior All extracted elements are treated equally regardless of extraction quality. ## Proposed Enhancement ```python element.metadata.confidence_score # 0.0 - 1.0 element.metadata.extraction_method # 'ocr', 'native', 'inferred' ``` This would significantly improve RAG quality for noisy document sources. Thank you!